Impact of vaccination justifications on compliance and social polarization: A repeated cross-sectional study in eight countries

Risk communication recommending infection prevention actions could encourage compliance but may intensify conflicts of opinion toward infection prevention actions. This study addressed five reasons that justify vaccination in COVID-19 and examined their impact on compliance intent and opinions as well as on bias in intergroup attitudes based on differences in opinions toward vaccination. The study was designed as four repeated cross-sectional online surveys covering eight countries (Japan, the United Kingdom, the United States, China, Korea, Germany, Italy, and South Africa). The survey periods covered July and October 2023 and January and April 2024 (post-pandemic). A modified Poisson regression analysis was conducted on the effect of justifications on compliance intent, and a multiple regression analysis was conducted on the impact of justifications on the opinions tendency. In addition, multiple regression analysis was conducted on the effect of justifications on intergroup bias based on disagreement, focusing on the vaccine-accepting group. The results showed that justifications for vaccination, such as preventing harm to others, self-protection, reducing the number of infections and deaths in society, and social norms, have ambivalent effects; they tend to promote compliance intent and opinions tendency while worsening attitudes toward those with different opinions about vaccination. However, the justifications because of penalties was confirmed to reduce negative attitudes toward those with different opinions, while not promoting compliance intent or opinions tendency toward vaccination. When risk communication using infection protection and social norm perspectives is conducted, it is important to simultaneously design and advocate interventions to mitigate intergroup conflicts based on opinions toward infection prevention actions. • Differences of opinion on vaccination lead to negative intergroup attitudes. • Negative attitudes are stronger among people who agree with vaccination. • Infection protection beliefs and social norms worsen vaccination opinion conflicts. • Penalties mitigate negative attitudes based on vaccination opinion.